The goals of this project are: 1) to identify the optimal envelope protein for vector preparation and to develop a strategy for preparing and concentrating y-globin lentiviral vector particles that allow efficient gene transfer into primitive human hematopoietic cells from patients with sickle cell disease and B-thalassemia that engraft in immunodeficient mice;2) to evaluate the safety of our y-globin lentiviral vector in cell culture and animal models and 3) to initiate a Phase I/II clinical gene therapy trial for severe B-thalassemia and sickle cell disease. Our Specific Aims are as follows: 1: to obtain therapeutic levels of globin lentiviral vectormediated gene transfer into primitive human hematopoietic cells;2: to evaluate the safety of globin lentiviral vectors using preclinical models;and 3: to evaluate stem cell-targeted, globin lentiviral vector-mediated gene transfer and expression in human patients with p-thalassemia intermedia, HbE-B-thalassemia, homozygous sickle cell anemia, or HbS-B-thalassemia. In pursuing the first aim, we will develop a producer cell clone for our y-globin lentiviral vector that yields high titer vector preparations and will develop methods for purifying and concentrating vector particles. We will also identify the appropriate envelope protein pseudotype that, after the purification and concentration of vector particles, insures efficient gene transfer into primitive human hematopoietic cells as assayed in an immunodeficient mouse model. Because the risk of insertional mutagenesis is inherent to the use of integrating retroviruses and has resulted in the development of leukemia in gene therapy trials, we have planned a comprehensive series of experiments to evaluate the safety of y-globin lentiviral vector-mediated gene transfer. Our preliminary data suggests that globin vectors are safer than vectors used in prior clinical trials because erythroid-specific, rather than powerful viral regulatory elements that are active in stem cells, are used to drive therapeutic gene expression. We propose to continue testing this hypothesis. We anticipate that the needed preclinical data from these first 2 specific aims will be obtained during the first 2-3 years of funding and will support a proposed phase I/II clinical gene therapy trial beginning in year 3, initially for patients with severe B-thalassemia who have a-globin excess, and then if success is achieved, for young adult patients with severe sickle cell disease. While our goal is that a clinical benefit will be obtained for individual patients, we are certain to learn important scientific information that will advance the likelihood of clinical success in future trials for the hemoglobin disorders. Our goals are relevant to public health and the mission of the National Heart, Lung and Blood Institute since the development of efficient stem cell targeted gene transfer would provide therapy for many inherited blood diseases. Because sickle cell disease causes severe symptoms, disability and often early death, curative therapies such as gene therapy are urgently needed.